Snowmobile suspension

ABSTRACT

A suspension system for a snowmobile comprises first and second suspension arms pivotally connected to a chassis and to a rail, and extending forwardly and upwardly from the rail. A bracket arm is fixedly connected to the first suspension arm. A link is pivotally connected to the bracket arm. A first shock absorber is pivotally connected to the first suspension arm and to the rail. The lower end of the first shock absorber is disposed forwardly of the lower end of the first suspension arm. A second shock absorber is pivotally connected to the link and to second suspension arm. The lower end of the second shock absorber is disposed rearwardly of the lower end of the first shock absorber. A tie rod is pivotally connected to the link, and to the second suspension arm. A snowmobile having such suspension system is also disclosed.

FIELD OF THE INVENTION

The present invention relates to suspension assemblies for trackedvehicles, and more particularly to rear suspension assemblies forsnowmobiles.

BACKGROUND OF THE INVENTION

Irregularities in the terrain over which a tracked vehicle travelsproduce displacements and deflections of its suspension system.Depending upon their magnitude, frequency and strength, thesedeflections cause more or less discomfort to the operator and passengerof the snowmobile.

The dynamic response of a rear suspension assembly of a tracked vehiclesuch as a snowmobile, to the multitude of loads imposed upon it duringoperation, has a significant effect on the overall performance of thevehicle and rider comfort. Different types of loads are regularlyexerted upon a tracked vehicle. A first type of loads results fromimpact loads imposed upon the rear suspension as the vehicle travelsover rough terrain and encounters bumps, these are of the most concern.A second type of loads results from loads resulting from accelerationand deceleration. The internal forces that are developed during rapidacceleration cause a weight transfer from the front of the vehicle tothe rear. This tends to lift the skis off the ground and thus interfereswith steering. The internal forces developed during rapid decelerationcause, however, a weight transfer from the rear of the vehicle to thefront. This tends to compress the front of the tunnel toward the frontof the slide rails. The complex interaction of the forces which occur inthe rear suspension assembly during operation have demanded optimaldesign of mechanisms for absorbing and attenuating the complexcombination of loads imposed upon a modern high performance snowmobile.

Conventionally, the rear suspension supports the endless track, which istensioned to surround a pair of parallel slide rails, a plurality ofidler wheels and at least one drive wheel or sprocket. A shock absorbingmechanism involving compressed springs, hydraulic dampers, and/or othershock absorbing elements, urges the slide frame assembly and the chassis(also known as a frame) of the snowmobile apart, against the weightsupported above the suspension in a static condition.

One example of a conventional rear suspension of a snowmobile isdescribed in U.S. Pat. No. 5,727,643, issued to Kawano et al. on Mar.17, 1998. Kawano et al. discloses a suspension device for providing aresilient support for a snowmobile body, including a frame forsupporting the snowmobile body. A slide rail is operatively connected tothe frame for pressing a crawler belt against a snow surface. A swingarm includes a first end pivotally supported on the frame and a secondend pivotally mounted on the slide rail. A shock absorber assemblyincludes a first end pivotally supported on a shaft adjacent to thefirst end of the swing arm, a second end of the shock absorber assemblybeing connected to the frame through a progressive link pivotallysupported on the swing arm.

Another example of a conventional rear suspension of a snowmobile isdisclosed in U.S. Pat. No. 5,904,216, issued to Furusawa on May 18,1999. Furusawa discloses a rear suspension of a snowmobile including twoangular suspension arm assemblies, which connect the slide frameassembly to the snowmobile chassis. These suspension arm assemblies aremoveable independently of one another in order to permit the slide frameassembly to react to static and dynamic forces arising during operation.A single cushion unit extends horizontally and is operatively connectedat opposed ends thereof to the respective suspension arm assemblies inorder to support and attenuate the loads.

Although conventional rear suspension systems available provide arelatively comfortable ride to the passengers, it is desirable tofurther improve the rear suspension assemblies for tracked vehicles,particularly snowmobiles. It is also desirable to provide a rearsuspension assembly that would be designed to reduce effects due toacceleration and deceleration loads.

SUMMARY OF THE INVENTION

It is an object of the present invention to ameliorate at least some ofthe inconveniences present in the prior art.

It is an object of the present invention to provide a rear suspensionassembly for a tracked vehicle, such as a snowmobile, which is connectedto a front suspension assembly so as to reduce the effect of weighttransfer during acceleration and deceleration. Motion of the suspensionassembly results in a force on the tunnel which counteracts the movementof the tunnel induced by the acceleration or the deceleration of thesnowmobile.

In one aspect, the invention provides a suspension system for asnowmobile having a chassis and an endless drive track. The suspensionassembly comprises a rail for engagement with the endless drive track. Afirst suspension arm has an upper end adapted for pivotally connectingto the chassis and a lower end pivotally connected to the rail. Thefirst suspension arm extends forwardly and upwardly from the rail. Asecond suspension arm is disposed rearwardly of the first suspensionarm. The second suspension arm has an upper end adapted for pivotallyconnecting to the chassis and a lower end pivotally connected to therail. The second suspension arm extends forwardly and upwardly from therail. A bracket arm has a first end and a second end. The first end ofthe bracket arm is fixedly connected to the first suspension arm betweenthe upper end and the lower end of the first suspension arm. A link hasa first end and a second end. The first end of the link is pivotallyconnected to the second end of the bracket arm. A first shock absorberhas an upper end and a lower end. The upper end of the first shockabsorber is pivotally connected to the first suspension arm. The lowerend of the first shock absorber is pivotally connected to rail. Thelower end of the first shock absorber is disposed forwardly of the lowerend of the first suspension arm. A second shock absorber has an upperend and a lower end. The lower end of the second shock absorber ispivotally connected to the second end of the link about a first pivotaxis. The first pivot axis is perpendicular to a longitudinal axis ofthe chassis. The upper end of the second shock absorber is pivotallyconnected to the second suspension arm. The lower end of the secondshock absorber is disposed rearwardly of the lower end of the firstshock absorber. A tie rod has a lower end and an upper end. The lowerend of the tie rod is pivotally connected to the link. The upper end ofthe tie rod is pivotally connected to the second suspension arm.

In an additional aspect, the tie rod is pivotally connected to thesecond end of the link about the first pivot axis.

In a further aspect, the second end of the bracket arm extends rearwadlyand downwardly from the first end of the bracket arm.

In an additional aspect, the first end of the link is pivotallyconnected to the second end of the bracket arm about a second pivotaxis. The second pivot axis is perpendicular to the longitudinal axis ofthe chassis. The second pivot axis is above of the first pivot axis.

In a further aspect, the first end of the bracket arm is fixedlyconnected to the front suspension arm at a point disposed upwardly ofthe second pivot axis.

In an additional aspect, the upper end of the first shock absorber ispivotally connected to the first suspension arm about a third pivotaxis. The third pivot axis is perpendicular to the longitudinal axis ofthe chassis. The lower end of the first suspension arm is pivotallyconnected to the rail about a fourth pivot axis. The fourth pivot axisis perpendicular to the longitudinal axis of the chassis. When thesnowmobile is at rest with no load applied thereon, a distance betweenthe second pivot axis and the fourth pivot axis is at least a third of adistance between the third pivot axis and the fourth pivot axis.

In a further aspect, the upper end of the front suspension arm isadapted for pivotally connecting to the chassis about a second pivotaxis. The second pivot axis is perpendicular to a longitudinal axis ofthe chassis. When the snowmobile experiences deceleration, an upwardreaction force is created at the second pivot axis.

In an additional aspect, the upper end of the front suspension arm isadapted for pivotally connecting to the chassis about a second pivotaxis. The second pivot axis is perpendicular to a longitudinal axis ofthe chassis. When the snowmobile experiences acceleration, a downwardreaction force is created on the second pivot axis.

In a further aspect, the upper end of second suspension arm is adaptedto be pivotally connected to the chassis via a fixed connection to alink, the link being adapted to be pivotally connected to the chassis.

In another aspect, the invention provides a snowmobile comprising achassis including a tunnel. The tunnel has a longitudinal axis. Anengine is disposed on the chassis. An endless drive track is disposedbelow the tunnel and is operatively connected to the engine forpropulsion of the snowmobile. Two skis are disposed on the frame, eachvia a front suspension. A straddle seat is disposed on the tunnel abovethe endless drive track. The straddle seat is disposed rearward of theengine. A rear suspension assembly supports and tensions the endlessdrive track. The rear suspension assembly includes a rail for engagementwith the endless drive track. A first suspension arm has an upper endpivotally connected to the tunnel and a lower end pivotally connected tothe rail. The first suspension arm extends forwardly and upwardly fromthe rail. A second suspension arm is disposed rearward of the firstsuspension arm. The second suspension arm has an upper end pivotallyconnected to the tunnel and a lower end pivotally connected to the rail.The second suspension arm extends forwardly and upwardly from the rail.A bracket arm has a first end and a second end. The first end of thebracket arm is fixedly connected to the first suspension arm between theupper end and the lower end of the first suspension arm. A link has afirst end and a second end. The first end of the link is pivotallyconnected to the second end of the bracket arm. A first shock absorberhas an upper end and a lower end. The upper end of the first shockabsorber is pivotally connected to the first suspension arm. The lowerend of the first shock absorber is pivotally connected to the rail. Thelower end of the first shock absorber is disposed forwardly of the lowerend of the first suspension arm. A second shock absorber has an upperend and a lower end. The lower end of the second shock absorber ispivotally connected to the second end of the link about a first pivotaxis. The first pivot axis is perpendicular to a longitudinal axis ofthe chassis. The upper end of the second shock absorber is pivotallyconnected to the second suspension arm. The lower end of the secondshock absorber is disposed rearwardly of the lower end of the firstshock absorber. A tie rod has a lower end and an upper end. The lowerend of the tie rod is pivotally connected to the link. The upper end ofthe tie rod is pivotally connected to the second suspension arm.

In an additional aspect, the tie rod is pivotally connected to thesecond end of the link about the first pivot axis.

In a further aspect, the tie rod and the link form an assembly throughwhich a pivot movement of the rear suspension arm relative to the railforces the bracket arm to act on the front suspension arm, therebymoving the front suspension arm.

In an additional aspect, the second end of the bracket arm extendsrearwadly from the first end of the bracket arm.

In a further aspect, the second end of the bracket arm extendsdownwardly from the first end of the bracket arm.

In an additional aspect, the first end of the link is pivotallyconnected to the second end of the bracket arm about a second pivotaxis. The second pivot axis is perpendicular to the longitudinal axis ofthe tunnel. The second pivot axis is upward of the first pivot axis.

In a further aspect, the first end of the bracket arm is fixedlyconnected to the front suspension arm at a point disposed upwardly ofthe second pivot axis.

In an additional aspect, the upper end of the first shock absorber ispivotally connected to the first suspension arm about a third pivotaxis. The third pivot axis is perpendicular to the longitudinal axis ofthe tunnel. The lower end of the first suspension arm is pivotallyconnected to the rail about a fourth pivot axis. The fourth pivot axisis perpendicular to the longitudinal axis of the tunnel. When thesnowmobile is at rest with no load applied thereon, a distance betweenthe second pivot axis and the fourth pivot axis is at least a third of adistance between the third pivot axis and the fourth pivot axis.

In a further aspect, the upper end of the front suspension arm ispivotally connected to the tunnel about a second pivot axis. The secondpivot axis is perpendicular to the longitudinal axis of the chassis.When the snowmobile experiences deceleration an upward reaction force iscreated on the second pivot axis.

In an additional aspect, the upper end of the front suspension arm ispivotally connected to the tunnel about a second pivot axis. The secondpivot axis is perpendicular to the longitudinal axis of the chassis.When the snowmobile experiences acceleration, a downward reaction forceis created on the second pivot axis.

In a further aspect, the upper end of the second suspension arm ispivotally connected to the tunnel via a fixed connection to a link. Thelink is pivotally connected to the tunnel.

For purposes of this application, terms related to spatial orientationsuch as forwardly, rearwardly, upwardly, downwardly, left, and right,are as they would normally be understood by a driver of the vehiclesitting thereon in a normal riding position.

Embodiments of the present invention each have at least one of theabove-mentioned object and/or aspects, but do not necessarily have allof them. It should be understood that some aspects of the presentinvention that have resulted from attempting to attain theabove-mentioned objects may not satisfy these objects and/or may satisfyother objects not specifically recited herein.

Additional and/or alternative features, aspects, and advantages ofembodiments of the present invention will become apparent from thefollowing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a left side elevational view of a snowmobile with a driver onthe snowmobile in a straddling position;

FIG. 2 is a perspective view taken from a front, left side of asuspension assembly according to a first embodiment of the invention;

FIG. 3 is a perspective view taken from a rear, left side of thesuspension assembly of FIG. 2 with a tunnel shown with some elementsremoved and the tunnel partially cut off added for clarity;

FIG. 4 is a left side elevational view of the suspension assembly ofFIG. 2;

FIG. 5 is a close-up view of the circled portion of the suspensionassembly of FIG. 2;

FIG. 6 is a left side elevational view of the suspension assembly ofFIG. 2 experiencing an acceleration of the snowmobile with a tunnel cutaway for clarity;

FIG. 7 is a left side elevational view of the suspension assembly ofFIG. 2 experiencing a deceleration of the snowmobile with a tunnel andsome portions of the suspension assembly cut away for clarity;

FIG. 8 is a perspective view taken from a rear, left side of asuspension assembly according to a second embodiment of the inventionshown with some elements removed and the tunnel partially cut off addedfor clarity

FIG. 9 is a close-up view of the circled portion of the suspensionassembly of FIG. 8; and

FIG. 10 is a left side elevational view of the suspension assembly ofFIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in detail to the drawings, and primarily to FIG. 1, asnowmobile incorporating the present invention is identified generallyby the reference numeral 100.

The snowmobile 100 includes a front end 102 and a rear end 104, whichare defined consistently with the forward travel direction of thevehicle. The snowmobile 100 includes a chassis 106 which normallyincludes a tunnel 108, an engine cradle portion 110 and a frontsuspension assembly portion 112. An engine 114 which is schematicallyillustrated, is carried by the engine cradle portion 110 of the chassis106. A ski and steering assembly is provided, in which two skis 116(only one of which is shown) are positioned at the front end 102 of thesnowmobile 100, and are attached to the front suspension assemblyportion 112 of the chassis 106 through a front suspension assembly 118.The front suspension assembly 118 includes ski legs 120, supporting arms122 and ball joints (not shown) for operatively joining the respectiveski legs 120, supporting arms 122 and a steering column 124. Thesteering column 124 at its upper end is attached to a steering devicesuch as a handlebar 126 which is positioned forward of a rider andbehind the engine 114 to rotate the ski legs 120 and thus the skis 116,in order to steer the vehicle.

An endless drive track 128 is positioned at the rear end 104 of thesnowmobile 100 and is disposed under the tunnel 108. The endless drivetrack 128 is operatively connected to the engine 114 through a belttransmission system 130 which is schematically illustrated by brokenlines. Thus, the endless drive track 128 is driven to run about a rearsuspension assembly 132 for propulsion of the snowmobile 100. The rearsuspension assembly 132 will be described in greater detail below.

At the front end 102 of the snowmobile 100, there are provided fairings134 that enclose the engine 114 and the belt transmission system 130,thereby providing an external shell that not only protects the engine114 and the belt transmission system 130, but can also be decorated tomake the snowmobile 100 more aesthetically pleasing. Typically, thefairings 134 include a hood and one or more side panels which are allopenable to allow access to the engine 114 and the belt transmissionsystem 130 when this is required, for example for inspection ormaintenance of the engine 114 and/or the belt transmission system 130. Awindshield 136 is connected to the fairings 134 near the front end 102of the snowmobile 100, or may be attached directly to the handlebar 126.The windshield 136 acts as a windscreen to lessen the force of the airon the rider while the snowmobile 100 is moving.

A seat 138 extends from the rear end 104 of the snowmobile 100 to thefairings 134. A rear portion of the seat 138 may include a storagecompartment, or may be used to accept a passenger seat. Two foot rests140 (only one of which is shown) are positioned on opposed sides of thesnowmobile 100 below the seat 138 to accommodate the rider's feet.

The endless drive track 128 is engaged with and driven by a drivesprocket (not shown) which is journaled by the tunnel 108 and is drivenby the engine 114 through the belt transmission system 130. The endlessdrive track 128 is suspended for movement relative to the chassis 106,by the rear suspension assembly 132. The rear suspension assembly 132includes a slide frame assembly 144 which primarily includes a pair ofspaced apart slide rails 146 that engage the inner side of theground-engaging portion of the endless drive track 128. The slide frameassembly 144 journals a plurality of backup rollers (not shown) and fouridler rollers 150. In addition, further rollers 152 are carried by thetunnel 108, in order to define the path over which the endless drivetrack 128 travels.

Referring to FIGS. 2 to 5, the rear suspension assembly 132 according toa first embodiment of the invention will now be described in greaterdetails. The rear suspension assembly 132 comprises left and right frontsuspension arms 154 and left and right rear suspension arms 164. It iscontemplated that the left and right rear suspension arms 164 could bewelded together to form a single rear suspension arm.

The front suspension arms 154 extend downwardly and rearwardly from afront portion 220 of the tunnel 108. Upper ends of the front suspensionarms 154 are pivotally attached to the tunnel 108 at pivot points 300 toform a pivot axis 301 (shown in FIG. 3) that is perpendicular to thelongitudinal axis 109 of the tunnel 108. The lower ends of the frontsuspension arms 154 are each pivotally attached to their respectiveslide rails 146 of the slide frame assembly 144 by a pivot pin assembly160 at pivot point 302. Left and right pivot points 302 define a pivotaxis 303 (shown in FIG. 3) perpendicular to the longitudinal axis 109 ofthe tunnel 108. The movement of the front portions of the slide rails146 relative to the tunnel 108 of the chassis 106 causes the frontsuspension arms 154 to rotate about the axis 301, relative to the tunnel108. The front suspension arms 154 are made of metal tubes having agenerally circular cross-section. It is contemplated that the frontsuspension arms 154 could have other cross-sections, and that the frontsuspension arms 154 could be of another material than metal.

The rear suspension arms 164 extend downwardly and rearwardly from arear portion 222 of the tunnel 108, and are disposed rearward of thefront suspension arms 154. The rear suspension arms 164 are made ofmetal tubes of a general circular cross-section. It is contemplated thatthe rear suspension arms 164 could have other cross-sections, and thatthe rear suspension arms 164 could be of another material than metal.The rear suspension arms 164 are pivotally attached to the tunnel 108 ofthe chassis 106 at pivot points 304 by means of a tube and shaftassembly. The tube and shaft assembly includes a tube 166 rotatablysupported by a shaft 168 which is mounted at the opposite ends thereofto the tunnel 108. The shaft 168 supports the rollers 152 supporting anupper portion of the endless drive track 128. Upper ends of the rearsuspension arms 164 are affixed to the tube 166 by welding for example,so that the rear suspension arms 164 are adapted to pivot about theshaft 168. The pivot points 304 and the shaft 168 define a pivot axis305 (shown in FIG. 3) perpendicular to the longitudinal axis 109 of thetunnel 108. Lower ends of the rear suspension arms 164 are fixedlyconnected to a hollow cross bar 172. The hollow cross bar 172 ispivotally connected to left and right rocker arms 174 at left and rightpivot points 306. The left and right pivot points 306 define a pivotaxis 307 (shown in FIG. 3) perpendicular to the longitudinal axis 109 ofthe tunnel 108. It is contemplated that each of rear rocker arms 174could be omitted and that each rear suspension arms 164 could bepivotally connected directly to the corresponding slide rail 146. Eachof the left and right rear rocker arms 174 is pivotally attached at itslower end to a rear portion of each slide rail 146 at pivot point 319.

Left and right rear blocks 170 are attached to the opposite ends of thehollow cross bar 172. Left and right rear stoppers 176 are attached totheir corresponding slide rails 146 at a position rearward of theircorresponding left and right rear rocker arms 174 in order to limit thepivot movement of the corresponding left and right rear rocker arms 174in the clockwise direction (as seen in FIG. 4). Each of the left andright rear stoppers 176 is mounted to a bracket 177 that is in turnmounted to the slide frame assembly 144. The left and right rearstoppers 176 could alternatively be the integral extensions of the slideframe assembly 144. The left and right blocks 170 are preferably made ofelastomer, such as rubber, polyurethane resin, delrin or nylon. The leftand right blocks 170 could alternatively be made of aluminum. In orderto attenuate the impact loads generated when the left and right rearblocks 170 collide with the corresponding left and right rear stoppers176, the rear stoppers 176 can be made of or coated with a resilientmaterial such as rubber or a polymer. Such a resilient material used onthe rear stoppers 176 also helps to reduce wear of the rear blocks 170.It is contemplated that the rear suspension assembly 132 could compriseleft and right front stoppers disposed forwardly from each of the leftand right rear rockers 174 to limit the pivot movement of the rearrocker arms 174 in the counterclockwise direction (as seen in FIG. 4).

The rear suspension arms 164 are coupled to the front suspension arms154 such that, in operation, a motion of the rear portion 222 of thetunnel 108 can induce a related motion of the front portion 220 of thetunnel 108. Coupling is ensured by connecting a rear shock absorber 196between the front suspension arms 154 and the rear suspension arms 164,as it will be described in greater details below. It is contemplated thecoupling could be ensured differently.

A front shock absorber assembly 180 disposed between the tunnel 108 andthe slide frame assembly 144 extends rearwardly and downwardly from thefront portion 220 of the tunnel 108. The front shock absorber assembly180 is disposed partially forward of the front suspension arms 154. Alower end of the first shock absorber assembly 180 is disposed forwardlyof the lower ends of the front suspension arms 154. The front shockabsorber assembly 180 is a damping unit which usually includes ahydraulic damper and a coil spring for absorbing the impact energy whenimpact forces are applied to the opposite ends of the damping unit. Thecoil spring biases the damping unit toward an extended position so thatthe hydraulic damper is in the best position to absorb the impactenergies. Since shock absorber assemblies of the type of the shockabsorber assembly 180 are well known in the art, it will not be furtherdescribed herein.

The front shock absorber assembly 180 is operatively attached at anupper end thereof to the tunnel 108 by a shaft and front bracketassembly comprising a shaft 183 and two brackets 182. The shaft 183 iswelded to the front suspension arms 154 and extends in an arcuate shapein between the front suspension arms 154. It is contemplated that theshaft 183 could not have an arcuate shape. The two brackets 182 arefixedly connected to the shaft 183 near a center of the shaft 183. Theupper end of the front shock absorber assembly 180 is pivotallyconnected to the brackets 182 at pivot points 308 such that an axialforce is applied to the upper end of the front shock absorber assembly180 when the front suspension arms 154 move with respect to the tunnel108. The pivot points 308 define a pivot axis 309 perpendicular to thelongitudinal axis 109 of the tunnel 108. The front shock absorberassembly 180 is pivotally connected to a lower end thereof to the slideframe assembly 144 via a shaft 184. The shaft 184 is fixedly connectedto the left and right slide rails 146, extending between them. The frontshock absorber assembly 180 is adapted to rotate about the shaft 184.The shaft 184 defines a pivot axis 310.

The rear shock absorber 196 extends forwardly and downwardly from therear portion 222 of the tunnel 108, and is disposed at least in partrearwardly of the front suspension arms 154. The rear shock absorber196, similar to the hydraulic damper of front shock absorber assembly180, is well known in the art, and therefore will not be described indetail. The rear shock absorber 196 is pivotally connected at its upperend to the tunnel 108 via a rear bracket 190 (shown in FIG. 2 anddescribed below) mounted on the tube 166 and shaft 168 assembly of therear suspension arms 164. The rear shock absorber 196 is connected at alower end to the front suspension arms 154 via a pivot connection toleft and right bracket arms 400 and the left and right links 402 (alldescribed in greater details below).

The rear bracket 190 is fixedly connected to the tube 166. As mentionedabove, the tube 166 is rotatable over the shaft 168. The rear bracket190 comprises two pins 192, 198 diametrically opposite to each other. Itis contemplated that the rear bracket 190 could be two rear brackets,each rear bracket comprising one of the pins 192, 198. The pin 192 ispivotally connected to the upper ends of the tie rods 188 at pivot point313. The pin 198 pivotally connects the rear bracket 190 to the upperend of the rear shock absorber 196 at pivot point 311.

The tie rods 188 are left and right tie rods disposed on each side ofthe rear shock absorber 196. A lower end of each of the left and righttie rods 188 is pivotally connected to a corresponding one of the leftand right links 402. An upper end of each of the left and right tie rods188 is pivotally connected to the pin 192 of the rear bracket 190. It iscontemplated that two pins 192 could be used to receive the upper endsof the left and right tie rods 188.

Upon motion of the rear suspension arms 164, the two pins 192, 198rotate with the tube 166 about the shaft 168 thereby actuating the rearshock absorber 196 and moving the left and right tie rods 188. The shockabsorber 196, the tie rods 188 and the links 402 form an assemblythrough which the pivot movement of the rear suspension arms 164 aboutthe shaft 168 and relative to the tunnel 108 of the chassis 106 forcesthe left and right bracket arms 400 to act on the front suspension arms154 thereby applying a force to the front portion 220 of the tunnel 108,and thereby actuating the front shock absorber assembly 180.

The left and right bracket arms 400 have upper ends fixedly connected toa shaft 401, and are disposed adjacent to each other, near a center ofthe shaft 401. The shaft 401 is fixedly connected, preferably bywelding, to the front suspension arms 154 at a location between thepivot axes 301 and 303. Second ends of the left and right bracket arms400 are pivotally connected to first ends of corresponding left andright links 402 at pivot points 312. The pivot points 312 define a pivotaxis 313 (shown in FIG. 5) perpendicular to the longitudinal axis 109 ofthe tunnel 108. Second ends of the left and right links 402 arepivotally connected to a corresponding one of the tie rods 188 at pivotpoints 314. The pivot points 314 define a pivot axis 315 (shown in FIG.5) perpendicular to the longitudinal axis 109 of the tunnel 108. It iscontemplated that the left and right links 402 could form a single link.

As best seen in FIG. 5, the position and dimension of the left and rightbracket arms 400 and the left and right links 402 are such that adistance B between the pivot axes 315 and 303 is at least A/3, when A isa distance between the pivot axes 301 and 303 computed when thesnowmobile 100 is in a neutral position. The neutral position is aposition of the snowmobile 100 when the snowmobile 100 is at restwithout load applied thereon (such as the weight of a driver orluggage).

Left and right torsion springs 200 are provided in order to push theslide frame assembly 144 apart from the tunnel 108 of the chassis 106,and to maintain the front and rear shock absorber assemblies 180, 196substantially in extended condition when no substantial loads areapplied thereon. The left and right torsion springs 200 surround anintermediate shaft 167 and are positioned at each end thereof. A firstfree end 201 (seen in FIG. 3) of each of the torsion springs 200 isabutting a second intermediate shaft 169, and a free second end 202thereof is abutting the slide frame assembly 144, under a preloadedcondition so that a predetermined torsion of force is applied to therear suspension arms 164, tending to pivot the rear suspension arms 164about the shaft 168 away from the tunnel 108 of the chassis 106. It iscontemplated that only one torsion spring could be used.

Left and right flexible tension straps 206 are attached at their upperends to the shaft 183, and are attached at their lower ends to the slideframe assembly 144 by means of a cross bar 208 which extends between andis attached at its opposite ends to the front ends of the slide rails146. The flexible tension straps 206 prevent the slide frame assembly144 from being pushed too far away from the tunnel 108.

Turning now to FIGS. 6 and 7, operation of the rear suspension assembly132 will be described.

FIG. 6 shows an arcuate solid arrow 454 indicating motion of the rearsuspension arms 164 and a straight solid arrow 450 showing movement ofthe rear portion 222 of the tunnel 108 when the snowmobile 100experiences acceleration with reference to the neutral position. When asnowmobile experiences acceleration, weight is transferred toward therear end of the snowmobile resulting in a downward movement of the rearportion of the tunnel. This weight transfer would normally result in anupward movement of the front portion of the tunnel, which can besometimes undesirable due to the reduction of weight on the front skis.However, the rear suspension assembly 132 of the present invention isdesigned to counteract this upward movement.

The rear suspension assembly 132 counteracts weight transfer by creatinga force that opposes the upward movement of the front portion 220 of thetunnel 108. The weight transfer induces the rear suspension arms 164 torotate toward the slide rails 146 (illustrated by the counterclockwiseoriented arcuate solid arrow 454). The motion of the rear suspensionarms 164 in turn compresses the rear shock absorber 196. Forces aretransferred to the left and right links 402 via the rear shock absorber196. This results in downward vertical forces 452 (only one of which isshown, illustrated by hatched arrow 452) acting on pivot points 300where the front suspension arms 154 connect to the tunnel 108. Thedownward forces 452 induce a rotation of the front suspension arms 164about the pivot axis 303 thus pulling the front portion 220 of thetunnel 108 toward the slide rails 146 and helping the tunnel 108 to keepa generally horizontal, or neutral orientation. Inducing movement of thetunnel 108 toward the slide rails 146 also induces the compression ofthe front shock absorber 180.

FIG. 7 shows an arcuate solid arrow 460 indicating motion of the rearsuspension arms 164 and a straight solid arrow 458 showing movement ofthe rear portion 222 of the snowmobile 100 when the snowmobile 100experiences decelerating with reference to the neutral position. When asnowmobile experiences deceleration, weight is transferred toward thefront end of the snowmobile which results in a downward movement of thefront portion of the tunnel. This will normally result in an upwardmovement of the rear portion of the tunnel, which can be sometimesundesirable do to the reduction of weight supported by the track whichprovides friction to slow down the snowmobile. However, the rearsuspension assembly 132 of the present invention is designed tocounteract this upward movement.

The rear suspension assembly 132 counteracts weight transfer by creatinga force that opposes the movement of the front portion 220 of the tunnel108. In contrast to acceleration, the weight transfer induced bydeceleration causes a rotation of the rear suspension arms 164 away fromthe slide rails 146 (illustrated by the clockwise oriented solidarcuated arrow 460). The rear shock absorber 196 thus extends and theforce is transferred to the left and right links 402 via the rear shockabsorber 196. This results in upward forces (illustrated by hatchedarrow 456, only one of which being shown) acting on pivot points 300where the front suspension arms 154 connect to the tunnel 108. Theupward forces 456 force the front suspension arms 154 to rotate aboutthe pivot axis 303, thus pushing the front portion 220 of the tunnel 108away from the slide rails 146 and helping the tunnel 108 to keep agenerally horizontal or neutral orientation.

Referring to FIGS. 8 to 10, a rear suspension assembly 132′ according toa second embodiment of the invention will now be described in greaterdetails. For ease of understanding, elements of the rear suspensionassembly 132′ similar to the rear suspension assembly 132 will have thesame reference numeral followed by a prime sign.

The rear suspension assembly 132′ comprises left and right frontsuspension arms 154′ and a single rear suspension arm 164′. It iscontemplated that the rear suspension assembly 132′ could comprise apair of rear suspension arms 164′.

The front suspension arms 154′ extend downwardly and rearwardly from thefront portion 220 of the tunnel 108. Upper ends of the front suspensionarms 154 are pivotally attached to the tunnel 108 at pivot points 300′to form a pivot axis 301′ that is perpendicular to the longitudinal axis109 of the tunnel 108. Lower ends of the front suspension arms 154′ areeach pivotally attached to their respective slide rails 146 of the slideframe assembly 144 at pivot point 302′. Left and right pivot points 302′define a pivot axis 303′ perpendicular to the longitudinal axis 109 ofthe tunnel 108. The movement of the front portions of the slide rails146 relative to the tunnel 108 of the chassis 106 causes the frontsuspension arms 154′ to rotate about the axis 301′, relative to thetunnel 108. The front suspension arms 154′ are made of metal tubeshaving a generally circular cross-section. It is contemplated that thefront suspension arms 154′ could have other cross-sections, and that thefront suspension arms 154′ could be of another material than metal.

The rear suspension arm 164′ extends downwardly and rearwardly from therear portion 222 of the tunnel 108, and is disposed rearward of thefront suspension arms 154′. The rear suspension arm 164′ is a metalpiece having a general rectangular cross-section. It is contemplatedthat the rear suspension arm 164′ could have other shapes ofcross-section, and that the rear suspension arm 164′ could be of anothermaterial than metal. An upper end of the rear suspension arm 164′ ispivotally connected to the tunnel 108 via a combination of a fixedconnection to a shaft 168′ and a pivot connection to two links 199′(only the left one being shown) as described below. It is contemplatedthat the upper ends of the rear suspension arm 164′ could instead beconnected to a tube and shaft assembly similar to the rear suspensionarms 164. The shaft 168′ has spline ends 169′ which fixedly connect tosecond ends of the links 199′ at points 157′. First ends of the links199′ are pivotally connected to the tunnel 108 at pivot points 304′. Thepivot points 304′ define a pivot axis 305′ perpendicular to thelongitudinal axis 109 of the tunnel 108.

A lower end of the rear suspension arm 164′ is fixedly connected to thehollow cross bar 172. The hollow cross bar 172 is pivotally connected tothe left and right rocker arms 174 at left and right pivot points 306′.The left and right pivot points 306′ define a pivot axis 307′perpendicular to the longitudinal axis 109 of the tunnel 108.

The rear suspension arm 164′ is coupled to the front suspension arms154′ by connecting a rear shock absorber 196′ between the frontsuspension arms 154′ and the rear suspension arm 164′, as it will bedescribed in greater details below. It is contemplated the couplingcould be ensured differently.

A front shock absorber assembly 180′ disposed between the tunnel 108 andthe slide frame assembly 144 extends rearwardly and downwardly from thefront portion 220 of the tunnel 108. The front shock absorber assembly180′ is disposed partially forward of the front suspension arms 154′. Alower end of the first shock absorber assembly 180′ is disposedforwardly of lower ends of the front suspension arms 154′. The frontshock absorber assembly 180′ is similar to the shock absorber assembly180 and will therefore not be described again.

The front shock absorber assembly 180′ is operatively attached at anupper end thereof to a front bracket assembly comprising a plate 183′and two brackets 182′. The plate 183′ is welded to the front suspensionarms 154′ and extends therebetween. It is contemplated that the plate183′ could not be a plate, and could be substituted by an actuate shaftsimilar to the shaft 183. The two brackets 182′ are fixedly connected tothe plate 183′ near a center of the plate 183′. The upper end of thefront shock absorber assembly 180′ is pivotally connected to thebrackets 182′ at pivot points 308′ such that an axial force is appliedto the upper end of the front shock absorber assembly 180′ when thefront suspension arms 154′ move with respect to the tunnel 108. Thepivot points 308′ define a pivot axis 309′ perpendicular to thelongitudinal axis 109 of the tunnel 108. The front shock absorberassembly 180′ is pivotally connected to a lower end thereof to the slideframe assembly 144 via the shaft 184. The front shock absorber assembly180′ is adapted to rotate about the shaft 184, which defines the pivotaxis 315′.

The rear shock absorber 196′ extends forwardly and downwardly from therear portion 222 of the tunnel 108, and is disposed at least in partrearwardly of the front suspension arms 154′. The rear shock absorber196′ is similar to the rear shock absorber assembly 180′ and willtherefore not be described again. The rear shock absorber 196′ isconnected at a lower end to the front suspension arms 154′ via a pivotconnection to left and right bracket arms 400′ and the left and rightlinks 402′ (all described in greater details below). The rear shockabsorber 196′ is pivotally connected at its upper end to two brackets198′. The brackets 198′ are fixedly connected partially to the shaft168′ and partially to the rectangular tube forming the rear suspensionarm 164′. It is contemplated that the rear bracket 198′ could be fixedlyconnected fully to the shaft 168′ or fully to the rectangular tubeforming the rear suspension arm 164′.

Two tie rods 188′ are disposed on each side of the rear shock absorber196′. Upper ends of the tie rods 188′ are pivotally connected tobrackets 192′ at pivot points 313′. The brackets 192′ are fixedlyconnected to the shaft 168′. The brackets 192′ are disposed on the shaft168′ at an angle with respect to the brackets 198′. Lower ends of thetie rods 188′ are pivotally connected to the links 402′ as will bedescribed below.

The left and right bracket arms 400′ have upper ends fixedly connectedto the plate 183′, and are disposed adjacent to each other, near acenter of the plate 183′. Second ends of the left and right bracket arms400′ are pivotally connected to first ends of corresponding left andright links 402′ at pivot points 312′. The pivot points 312′ define apivot axis 313′ perpendicular to the longitudinal axis 109 of the tunnel108. Second ends of the left and right links 402′ are pivotallyconnected to the lower end of the rear shock absorber 196′ at pivotpoints 314′ or 403′. The pivot points 314′ define a pivot axis 315′perpendicular to the longitudinal axis 109 of the tunnel 108. Contrarilyto the first embodiment, the second ends of the left and right links402′ are not pivotally connected to corresponding left and right tierods 188′. Instead, the left and right tie rods 188′ connect to a middleof a corresponding link 402′ at pivot points 321′ or 403′. As aconsequence, a pivot axis of the lower end of the shock absorber 196′ isdifferent from a pivot axis of the lower end of the tie rods 188′. Pivotpoint 403′ enables the suspension characteristics to be modified toadjust to personal preference. It is contemplated that the points 321′,314′ and 403′ could be curved slots instead of individual points toallow for many easily-adjustable different positions of the lower endsof the tie rods 188′ or shock absorber 196′.

Similarly to the first embodiment, the position and dimension of theleft and right bracket arms 400′ and the left and right links 402′ aresuch that a distance B between the pivot axes 315′ and 303′ is at leastA/3, when A is a distance computed at the neutral position between thepivot axes 301′ and 303′.

Left and right torsion springs 200′ (only the right one being shown inFIG. 8) are provided in order to push the slide frame assembly 144 apartfrom the tunnel 108 of the chassis 106, and to maintain the front andrear shock absorber assemblies 180′, 196′ substantially in extendedcondition when no substantial loads are applied thereon. The left andright torsion springs 200′ surround the shaft 168′ and are positioned oneach side of the rear suspension arm 164′. A first free end (not shown)of each of the torsion springs 200 is abutting the shaft 168′, and afree second end (not shown) thereof is abutting the slide frame assembly144, under a preloaded condition so that a predetermined torsion offorce is applied to the rear suspension arm 164′, tending to pivot therear suspension arm 164′ about the links 199′ away from the tunnel 108of the chassis 106. It is contemplated that only one torsion springcould be used.

Left and right flexible tensions straps 206′, similar to the flexiblestraps 206, are attached at their upper ends to the plate 183′, and attheir lower ends to the slide frame assembly 144 by means of the shaft184.

Operation of the rear suspension assembly 132′ is substantially similarto the operation of the rear suspension assembly 132 except for theabsence of the rotation at the tube 166 and shaft 168 that has beensubstituted by the link 199′ pivoting with respect to the tunnel 108.Upon motion of the rear suspension arm 164′, the rear shock absorber196′ is actuated and the left and right tie rods 188′ move. The links199′, the rear shock absorber 196′, the tie rods 188′ and the links 402′form an assembly through which the pivotal movement of the links 199′(and therefore the rear suspension arm 164′) about the pivot axis 305′and relative to the tunnel 108 of the chassis 106, forces the left andright bracket arms 400′ to act on the front suspension arms 154′ therebyapplying a force to the front portion 220 of the tunnel 108, and therebyactuating the front shock absorber assembly 180′.

Modifications and improvements to the above-described embodiments of thepresent invention may become apparent to those skilled in the art. Theforegoing description is intended to be exemplary rather than limiting.The scope of the present invention is therefore intended to be limitedsolely by the scope of the appended claims.

What is claimed is:
 1. A snowmobile comprising: a chassis including atunnel, the tunnel having a longitudinal axis; an engine disposed on thechassis; an endless drive track disposed below the tunnel andoperatively connected to the engine for propulsion of the snowmobile;two skis disposed on the chassis, each via a front suspension; astraddle seat disposed on the tunnel above the endless drive track, thestraddle seat being disposed rearward of the engine; and a rearsuspension assembly supporting and tensioning the endless drive track,the rear suspension assembly including: a rail for engagement with theendless drive track; a first suspension arm having an upper endpivotally connected to the tunnel and a lower end pivotally connected tothe rail, the first suspension arm extending forwardly and upwardly fromthe rail; a second suspension arm disposed rearward of the firstsuspension arm, the second suspension arm having an upper end pivotallyconnected to the tunnel and a lower end pivotally connected to the rail,the second suspension arm extending forwardly and upwardly from therail; a bracket arm having a first end and a second end, the first endof the bracket arm being fixedly connected to the first suspension armbetween the upper end and the lower end of the first suspension arm; alink having a first end and a second end, the first end of the linkbeing pivotally connected to the second end of the bracket arm above thefirst suspension arm at a link pivot axis; a first shock absorber havingan upper end and a lower end, the upper end of the first shock absorberbeing pivotally connected to the first suspension arm, the lower end ofthe first shock absorber being pivotally connected to the rail, and thelower end of the first shock absorber being disposed forwardly of thelower end of the first suspension arm; a second shock absorber having anupper end and a lower end, the lower end of the second shock absorberbeing pivotally connected to the second end of the link about a firstpivot axis, the first pivot axis being perpendicular to a longitudinalaxis of the chassis, the first pivot axis being located between theupper and lower ends of the first suspension arm, the first pivot axisbeing disposed such that the first suspension arm is disposed betweenthe first pivot axis and the link pivot axis, the upper end of thesecond shock absorber being pivotally connected to the second suspensionarm; and a tie rod having a lower end and an upper end, the lower end ofthe tie rod being pivotally connected to the link, and the upper end ofthe tie rod being pivotally connected to the second suspension arm. 2.The snowmobile of claim 1, wherein the tie rod is pivotally connected tothe second end of the link about the first pivot axis.
 3. The snowmobileof claim 2, wherein the tie rod and the link form an assembly throughwhich a pivot movement of the rear suspension arm relative to the railforces the bracket arm to act on the first suspension arm, therebymoving the first suspension arm.
 4. The snowmobile of claim 2, whereinthe second end of the bracket arm extends rearwardly from the first endof the bracket arm.
 5. The snowmobile of claim 2, wherein the second endof the bracket arm extends downwardly from the first end of the bracketarm.
 6. The snowmobile of claim 2, wherein the first end of the link ispivotally connected to the second end of the bracket arm about the linkpivot axis, the link pivot axis being perpendicular to the longitudinalaxis of the tunnel, and the link pivot axis is upward of the first pivotaxis.
 7. The snowmobile of claim 6, wherein the first end of the bracketarm is fixedly connected to the first suspension arm at a point disposedupwardly of the link pivot axis.
 8. The snowmobile of claim 6, whereinthe upper end of the first suspension arm is adapted for pivotallyconnecting to the chassis about a second pivot axis, the upper end ofthe first shock absorber is pivotally connected to the first suspensionarm about a third pivot axis, the third pivot axis being perpendicularto the longitudinal axis of the tunnel, and the lower end of the firstsuspension arm is pivotally connected to the rail about a fourth pivotaxis, the fourth pivot axis being perpendicular to the longitudinal axisof the tunnel; and wherein, when the snowmobile is at rest with no loadapplied thereon, a distance between the link pivot axis and the fourthpivot axis is at least a third of a distance between the second pivotaxis and the fourth pivot axis.
 9. The snowmobile of claim 2, whereinthe upper end of the first suspension arm is pivotally connected to thetunnel about a second pivot axis, the second pivot axis beingperpendicular to the longitudinal axis of the chassis; and wherein whenthe snowmobile experiences deceleration an upward reaction force iscreated on the second pivot axis.
 10. The snowmobile of claim 2, whereinthe upper end of the first suspension arm is pivotally connected to thetunnel about a second pivot axis, the second pivot axis beingperpendicular to the longitudinal axis of the chassis, and when thesnowmobile experiences acceleration, a downward reaction force iscreated on the second pivot axis.
 11. The snowmobile of claim 2, whereinthe upper end of the second suspension arm is pivotally connected to thetunnel via a fixed connection to a link, the link being pivotallyconnected to the tunnel.